The present invention relates generally to a stackable weight plate and weight stack apparatus employing a plurality of the weight plates for use in a weight lifting exercise machine.
There are two basic types of weight plate used in resistance training. The first type consists of free weights used on barbells and dumbbells, which are usually hand held but which can be loaded on a machine. The second type are generally known as selector weights, which are always attached to exercise machines.
Free weights are one of the earliest forms of weight plates used in resistance training or exercising. They are usually circular in shape, and have a central aperture which allows them to be fitted on a round, bar type handle or machine mounted receiver. They typically come in multiple weight increments, and can be loaded or unloaded by the user in order to increase or decrease the resistance during an exercise. This is dangerous, cumbersome, and requires repeated loading and unloading during the course of an exercise routine. It also requires the exerciser to have a quantity of free weight plates on hand. Often, in a health clubs, the weight plates will be moved from one station to another, and it can be hard to locate a specific plate when needed. U.S. Design Pat. No. 406,183 of Zovich illustrates a typical free weight plate of generally circular shape.
Selector weights are stacked one plate on top of another and are a permanent part of a weight lifting exercise machine. A typical weight stack consists of a series of stacked weight plates each with a central opening, and a selector stem engaging through the central openings of the stacked plates. The selector stem has a series of holes, one for each weight in the stack. The stem is attached to the top plate in the stack and protrudes downwards through the stack, and the top plate is linked via a cable and pulley assembly to one or more exercise stations. Each plate has a transverse opening extending from the front of the stack through to the central opening. A selector pin can be inserted through any selected weight in the stack and into the aligned hole in the selector stem. The selected weight and all weights above it in the stack will then be lifted. The amount of resistance can easily be adjusted by removing the pin and inserting it through a higher or lower weight in the stack, decreasing or increasing the resistance, respectively. The pin therefore selects the number of plates to be lifted.
Weight stacks usually travel up and down on a slide or guide rod system, and are connected to a movable exercise member by means of a linkage system such as a belt and pulley, cable and pulley, pivoting linkage, rigid lever arm, or the like.
The selector weights generally come only in relatively large increments of 5, 10, 15, and 20 lbs, for example. Thus, add-on or incremental weights are often provided to allow the exerciser to adjust the weight stack in smaller increments. Thus, if a person using a weight stack with ten pound increments could not make a ten pound step up in resistance, they could add a five pound add-on or incremental weight on top of the stack to increase the resistance by half a step. Normally, add-on weights are not connected in any way to the machine and must be placed on and off the weight stack by the user. These weights can shift during movement and rub against the weight stack guide rods. This will create friction or drag which can be felt by the user.
Selector weight plates are typically made from steel flat bar or cast iron. Steel plates are cut from flat bar stock into a generally rectangular shape. Cast iron plates are poured from molten iron and are also usually rectangular in shape. In all cases, the rear edge or face of the plate is straight and the side edges are at 90 degrees to the rear face. Weight stacks of rectangular weight plates are described in U.S. Pat. No. 5,374,229 of Sencil, U.S. Pat. No. 5,308,304 of Habing, and U.S. Pat. No. 5,779,601 of Ish, III, for example. Some selector weight plates are provided with locating or nesting devices to keep the weights aligned with one another when stacked. One common nesting device is a button and hole device, in which one or two buttons on the top of one weight plate nest into holes located on the underside of another weight plate. Another nesting arrangement involves interlocking sleeves which engage in the central opening of a weight plate and which have a series of ridges and valleys which mate when one weight plate is placed on top of another. The purpose of such nesting arrangements is to help align the plates as they are stacked, and also to prevent shifting or twisting of one plate relative to another during use.
The problem with the button and hole type of nesting arrangement is that the shape and size of the buttons is such that they do not provide much help in preventing the weights from shifting or twisting from side to side. Because the buttons and holes are in line with the guide rods, any shifting will cause the guide rod holes to rub against the guide rods before the buttons can prevent it. This creates friction and causes the exerciser to feel drag in the exercise movement. Also, since the buttons must be cast or molded into the weights, the weight plates are not uniform in thickness. In a casting process, it is preferable for the molds to be a uniform thickness so that molten material is allowed to flow unobstructed through the mold cavity. Any variation could cause the molten iron not to fill the button-forming recess. A less than perfect pour could cause the buttons and holes not to align.